1. Field of Invention
The invention relates to providing electrical power to a plurality of low voltage electrical loads, and more particularly to a string of lights includes a load comprising a plurality of lamps connected in series, the lamps comprising a first group of lamps including an LED and a first Zener diode in parallel therewith, and a second group of lamps including an incandescent light bulb and a second Zener diode in parallel therewith in which the first group of lamps are alternate with the second group of lamps.
2. Description of Related Art
LEDs are renowned for their long life and their ability to resist shock. Also, an LED consumes much less electrical power than fluorescent lamps (i.e., energy saving). Therefore, LED lighting devices are gaining popularity worldwide.
A typical string of lights including a plurality of LED bulbs arranged electrically in a series circuit is shown in FIG. 1. AC (alternating current) 120V is rectified by a full-wave rectifier (e.g., bridge rectifier as shown) to convert into DC (direct current) to be consumed by the plurality of LED bulbs. However, the well known light string suffers from a disadvantage. In detail, one LED bulb of the string burning out will kill the circuit. For example, the light string comprises 40 blue LED bulbs of 3V 0.02 A. Any burned out blue LED bulb will kill the circuit with the remaining 39 blue LED bulbs being disabled.
A typical string of lights including a plurality of (e.g., 40) incandescent light bulbs arranged electrically in a series circuit is shown in FIG. 2. AC 120V is fed to the 40 incandescent light bulbs for consumption. However, the well known light string suffers from a disadvantage. In detail, one incandescent light bulb of the string burning out will kill the circuit. For example, the light string comprises 40 incandescent light bulbs of 3V 0.1 A. Any burned out incandescent light bulb will kill the circuit with the remaining 39 incandescent light bulbs being disabled.
Another typical string of lights including a plurality of (e.g., 35) white LED bulbs of 3.2V 0.02 A arranged electrically in a parallel circuit is shown in FIG. 3. AC 120V is rectified by a full-wave rectifier 15 to convert into DC to be consumed by the plurality of white LED bulbs.
However, the well known light string still suffers from a disadvantage. In detail, electric current is required to increase as the number of white LED bulbs increases. The total current (e.g., I) of the circuit can be expressed as a multiplication of current (e.g., If) flowing through each white LED bulb times the number of white LED bulbs (e.g., N). As shown, AC 120V is rectified by the full-wave rectifier 15 to convert into DC (e.g., DC 3.2V 0.7 A) to be consumed by the 35 white LED bulbs. For example, operating voltage of the white LED bulb is 3.2V and operating current thereof is 0.02 A. Hence, the total current (I) is 0.02 A×35 equal to 0.7 A. Advantageously, the circuit will maintain its normal operation if, for example, one white LED bulb is burned out. That is, the remaining 34 white LED bulbs still emit light. However, cost of developing such type of full-wave rectifier capable of converting, for example, AC 120V into DC (e.g., DC 3.2V 0.7 A) to be consumed by the LED bulbs is very high. Hence, it may adversely affect competitiveness of such light string in the market.
Another typical string of lights including a plurality of (e.g., 35) incandescent light bulbs of 3.2V 0.08 A arranged electrically in a parallel circuit is shown in FIG. 4.
However, the well known light string still suffers from a disadvantage. In detail, electric current is required to increase as the number of incandescent light bulbs increases. As shown, AC 120V is rectified by a full-wave rectifier 15 to convert into DC (e.g., DC 3.2V 2.8 A) to be consumed by the 35 incandescent light bulbs. For example, operating voltage of the incandescent light bulb is 3.2V and operating current thereof is 0.08 A. Hence, the total current (I) is 0.08 A×35 equal to 2.8 A. Advantageously, the circuit will maintain its normal operation if, for example, one incandescent light bulb is burned out. That is, the remaining 34 incandescent light bulbs still emit light. However, cost of developing such type of full-wave rectifier capable of converting, for example, AC 120V into DC (e.g., DC 3.2V 2.8 A) to be consumed by the incandescent light bulbs is very high. Hence, it may adversely affect competitiveness of such light string in the market.
There have been numerous suggestions in prior patents for light string. For example, U.S. Pat. No. 6,344,716 discloses a Christmas light string. Thus, continuing improvements in the exploitation of light string are constantly being sought.